Michels W M, Grootendorst D C, Rozemeijer K, Dekker F W, Krediet R T
Division of Nephrology, Department of Medicine, Academic Medical Center, University of Amsterdam, Amsterdam,The Netherlands.
Clin Nephrol. 2009 Nov;72(5):337-43. doi: 10.5414/cnp72337.
Measuring GFR using exogenous markers without a bladder catheter, errors can be easily made due to incomplete urine collection. The aim was to quantify agreement for 125I-iothalamate GFR measurements with and without a correction for inaccurate urine collection using 131I-hippuran.
The last available GFR measurement of adult patients was included. GFR was measured in two subsequent clearance periods with 125I-iothalamate by the standard method with correction for inaccurate urine collections using 131I-hippuran. The uncorrected and corrected GFR measurements were compared within and between the time periods for each individual patient. To study the agreement between both methods, intraclass correlation coefficients (ICC) were calculated and Bland-Altman plots, with accompanying accuracies and precisions, were used. Cohen's kappa was calculated to analyze the agreement of both methods for classifying patients according to the stages of chronic kidney disease (CKD).
For the 332 stable included patients, the mean GFR of the uncorrected measurements was 77.8 ml/min (34.7) and the mean GFR of the corrected measurements was 81.0 ml/min (34.9). The ICC was 0.80 for the uncorrected measurements with an accuracy of 7.3 ml/min and a precision of 21.7 ml/min. For the corrected GFR measurements the ICC was 0.98, with an accuracy of 2.1 ml/min and a precision of 6.5 ml/min. Comparison between the methods showed an ICC of 0.95, an accuracy of 3.2 and a precision of 11.0. In total, 86% of the patients were classified similarly into CKD stages with both methods, overall Cohen's kappa was 0.81.
Agreement was better for GFR measurements corrected for inaccurate urine collections. Therefore, GFR measurements with 125I-iothalamate should be corrected for inaccurate urine collections using 131I-hippuran. Without such correction the GFR is easily underestimated which may lead to overtreatment.
在使用外源性标志物测量肾小球滤过率（GFR）且不使用膀胱导管的情况下，由于尿液收集不完全，很容易出现误差。目的是量化使用125I-碘他拉酸盐测量GFR时，在使用131I-马尿酸对不准确尿液收集进行校正和未校正两种情况下的一致性。
纳入成年患者最后一次可用的GFR测量值。在两个连续的清除期内，采用标准方法用125I-碘他拉酸盐测量GFR，并使用131I-马尿酸对不准确的尿液收集进行校正。对每位患者在不同时间段内以及时间段之间的未校正和校正后的GFR测量值进行比较。为研究两种方法之间的一致性，计算组内相关系数（ICC），并使用Bland-Altman图以及相应的准确性和精密度。计算Cohen's kappa系数以分析两种方法根据慢性肾脏病（CKD）分期对患者进行分类的一致性。
对于纳入的332例稳定患者，未校正测量的平均GFR为77.8 ml/min（标准差34.7），校正后测量的平均GFR为81.0 ml/min（标准差34.9）。未校正测量的ICC为0.80，准确性为7.3 ml/min，精密度为21.7 ml/min。校正后的GFR测量ICC为0.98，准确性为2.1 ml/min，精密度为6.5 ml/min。两种方法之间的比较显示ICC为0.95，准确性为3.2，精密度为11.0。总体而言，86%的患者使用两种方法被相似地分类到CKD分期，整体Cohen's kappa系数为0.81。
对不准确尿液收集进行校正后的GFR测量一致性更好。因此，使用125I-碘他拉酸盐测量GFR时，应使用131I-马尿酸对不准确的尿液收集进行校正。若不进行此类校正，GFR很容易被低估，这可能导致过度治疗。
